1. Field of the Invention
The present invention relates to data communications and more particularly to a Fibre Channel (FC) switch.
2. Description of the Related Art
Fibre Channel (FC) switches are used to connect servers to storage services and resources, for creating a storage area network (SAN). In computing, a storage area network (SAN) is a network designed to attach computer storage devices such as disk array controllers and tape libraries to servers. The SAN fabric is an active intelligent interconnection scheme that utilizes the Fibre Channel Architecture. Servers and storage devices connect to FC SAN switches as an N_Port (node port), while the switch provides an F_Port (fabric port). When two FC SAN switches are connected together to enlarge the switch fabric, they will utilize an unique port type, an E-Port on each end. E_Ports implement a unique mechanism to exchange configuration and topology information between the switches.
When the E_Ports of two switches support the same configuration and protocol parameters, they will establish an inter-switch link (ISL) between the two switches. In contrast, when the E_Ports of two switches do not support the same configuration and protocol parameters, or when there are other incompatible factors between the two switches, no ISL link will be established. There is no method for directly connecting switches that do not share a common ISL protocol. The industry standard for ISLs is defined in the T11 FC-SW-2 standard. Currently each FC switch vendor provides various extensions to the basic FC architecture in order to provide value added capabilities to their switches. These vendor-provided extensions cause these switches to be unable to establish a link with switches that do not support the same set of extensions. This lack of interoperability between dissimilar FC switches is a major impediment to deploying new FC technology into existing SANs.
ISLs established through E_Ports, as described above, have additional unique properties related to maintaining a consistent view of the fabric and the various devices among all the interconnected SAN switches. Any device with an E_Port connection to the SAN is a peer with all the switches, which are collectively managing and controlling the SAN itself. An alteration of an E_Port link will disrupt the SAN fabric management structure, and consequently can cause a momentary disruption across the entire SAN, while the interconnected switches re-establish the management hierarchy and restore the switch to switch communications. Accordingly, inter-switch links expose the SAN to disruptions from events that would be trivial if occurring on a normal device link (e.g., N_Port). For example, the routing tables must be changed in all switches within the fabric when any E_Port connection is altered.
Another problem associated with inter-switch links is management security risk. As all switches are peers in the management of the SAN, management control of any single switch on the SAN will provide management control of the entire SAN. The Inter-switch links extend the SAN, as well as the risk of unwanted SAN management access, to every connected switch in the fabric. Consequently, there is no way to aggregate server or device FC connections directly from one FC switch to another without extending the security risk as well.
Potential solutions are to enforce a homogeneous SAN switch environment or insert a “router” function between the SANs. The SAN can remain homogeneous by deploying only one vendor's switch product or requiring all FC switches in the SAN to operate in a standard mode (e.g., FC-SW-2 mode). However, changing to the FC-SW-2 mode (also known as open mode) is disruptive to the SAN, requires operational changes to the management of the SAN and disables features that can be selected and used in the vendor's private extensions. Inserting a router between two switches introduces a performance characteristic that can lead to performance and scalability limitations. Each message crossing the SAN must be interrogated, and if appropriate, retransmitted to the other SAN segments. The equipment necessary to perform this task remains expensive for the performance levels needed in a large SAN.
In addition, the management of the storage environment is divided at a router. The storage devices and servers on one side of the router cannot see the storage devices and servers on the other side through the router; instead each can only see the router. The router itself must then be explicitly configured and managed in order to make the proper devices visible across the router, to pass the proper traffic across the router, and to map resource addresses from one side to the other. This is similar to a network router performing Network Address Translation (NAT). It is therefore desirable to have a system and method that minimizes switch interoperability impediments, management control risks, and management control points, while still providing access for multiple servers to access the SAN through a single physical port connection.